The corrosion of metal surfaces is a serious problem, particularly when such metal surfaces are exposed to water, rain, or snow, subjected to conditions of high humidity, or confronted with an atmosphere high in acidic materials. Most metals are susceptible to varying degrees of corrosion that will significantly affect the quality of such metals, as well as that of the products produced from them. Such corrosion problems are of primary importance not only in the ferrous metal field, but also for many of the non-ferrous metals. In addition, when polymer coatings such as paints, adhesives, or rubbers are applied to the metal, corrosion of the base metal material may cause a loss of adhesion between the polymer coating and the base metal.
Polymeric coatings, such as sprayable polymer coatings, have been used as a form of protection against corrosion and wear for metal substrates. With the increase in recycling of post-consumer waste plastics in recent years, plastic containers made from polypropylene, polystyrene, polyvinylchloride, polyethylene terephthalate, etc., have been recycled back into post-consumer commingled plastic coatings, which can have applications in protective coatings for metal substrates. Typically, the recycling may involve melt-compounding the commingled plastics to form a continuous phase. During the process, the commingled plastics can also be blended with other polymers to obtain the desired mechanical properties. A major challenge during this blending process is overcoming the immiscibility of the different polymeric species. Due to differences in surface tension between the different polymeric species in the blend, limited diffusion can occur between incompatible species, thereby weakening the cohesive strength between the immiscible polymer species. A variety of compatibilization methods for commingled plastics have been proposed, mostly based on the addition or generation of block copolymers at the interface between the different polymer species. However, these techniques are typically not cost-effective, since block copolymers are usually made by chemically sophisticated synthetic routes. Current available compatibilizers, such as linear block copolymers, are also deficient in that they result in inadequate cohesive strength at the interface, thereby producing polymer blend coatings that are susceptible to cracking.
Corrosion of the underlying metal substrate may occur due to abrasion of the coating or due to formation of cracks within the coating. A crack in such a coating typically leads to corrosion of the underlying metal, resulting in expensive and wasteful repair or replacement of some or all of the metal substrate. A coating with a self-healing property would self-heal upon its physical compromise. Therefore, self-healing agents may be incorporated into the coating. These agents can fill cracks or inhibit corrosion when the coating is damaged. Thus, it is desirable to develop self-healing coatings from polymer blends, including recycled polymers, that contain corrosion inhibitors or crack-healing agents.